1. Field of the Invention
The present invention relates to an apparatus and method for uniformly treating an article with plasma.
2. Description of Related Art
U.S. Pat. Nos. 5,227,180, 5,236,636 and 5,415,819, assigned to the assignee of the present invention and incorporated herein by reference, disclose apparatus and methods for plasma treating an article between two or more electrodes which together form a plasma treatment chamber. These electrode-defined chambers offer several advantages over conventional plasma treatment chambers having discrete electrodes positioned therein. For example, by eliminating the need for a separate chamber to house the electrodes, smaller treatment volumes or spaces may be provided. The treatment spaces may be further reduced by conforming the electrodes to the shape of the article or articles to be treated. These relatively small treatment spaces may be quickly evacuated by low-cost vacuum pumps, decreasing the cycle times and increasing the efficiency of the process relative to conventional plasma treatment processes.
One challenge associated with both conventional plasma treatment processes and the processes taught in U.S. Pat. Nos. 5,227,180, 5,236,636 and 5,415,819 is that of obtaining a uniformly treated article surface. It is possible, using electrode-defined chambers, to create an electric field throughout the treatment chamber. However, because plasma generation requires the presence of both an electric field and an ionizable gas, if the ionizable gas is not sufficiently distributed over an article's surface, the surface will not be uniformly treated. The relatively small treatment volumes and correspondingly rapid treatment times that make the use of electrode-defined chambers desirable, also add to the challenge of achieving a uniform surface treatment. The residence times of ionizable gas molecules within these chambers are shorter than in conventional treatment chambers, limiting the amount of diffusion that can occur. The present inventors have discovered that conventional inlet ports may not provide optimal distribution of the ionizable gas within these electrode-defined chambers.